A 'Catch All' email account is basically a special kind of email alias that allows you to receive email to ANY email address on your domain.

Setting an email account to be a 'Catch All' account will mean that not only will it collect email for the email address specified, but for any other mail sent to the domain that does not have a appropriate email account or email forward set up for.

For example if a mail was sent to anythiing@mydomain.com and this address was not setup for a specific account, then the 'Catch All' email account will collect this mail instead.

You can automatically create, delete and modify 'Catch All Email' right from the Server Intellect control panel.

See How do I configure an Email Account as a Catch All?